1. Field of the Invention
This invention relates generally to a method of forming a multilayer article, and more particularly to a method for depositing multiple layers on an article with a plasma generated by an arc between a cathode and an anode.
2. Description of the Related Art
Plastics and other polymers are commercially available materials possessing physical and chemical properties which are useful in a wide variety of applications. For example, polycarbonates are a class of polymers which, because of their excellent breakage resistance, have replaced glass in many products, such as automobile head-lamps, safety shields, eyewear, and windows. However, many polycarbonates also have properties which may be disadvantageous in some applications, such as low abrasion resistance and susceptibility to degradation from exposure to ultraviolet (UV) light. Thus, polycarbonates are not commonly used in applications such as automotive and other windows which are exposed to ultraviolet light and physical contact from a variety of sources.
To minimize the problems of low abrasion resistance and UV degradation, known methods of treating polycarbonates involve the application of layers of abrasion resistant material and UV absorbing material to the polycarbonate substrate. For example, U.S. Pat. No. 5,156,882 to Rzad et al. discloses a method of preparing transparent plastic articles having an improved protective stratum which provides protection from UV light and abrasion. The article includes a polycarbonate substrate and a multi-layered coating applied to the polycarbonate substrate by plasma enhanced chemical vapor deposition (PECVD). Plasma enhanced chemical vapor deposition is a significant improvement over conventional chemical vapor deposition (CVD) because PECVD can be used to deposit materials on plastic substrates such as polycarbonates, which was generally not feasible with CVD at temperatures lower than the glass transition temperature of the plastic. In PECVD, the applied electric field enhances the formation of the ionized species, providing a much higher percentage of ionized species which thereby permits the use of low deposition temperatures, e.g. as low as room temperature.
Another method of treating polycarbonates involves the application of what is conventionally known as a silicone hardcoat to the polycarbonate substrate. Examples of silicone hardcoats are described, for example, in U.S. Pat. Nos. 4,842,941; 4,927,704; and 5,051,308, incorporated herein by reference. The silicone hardcoat is applied in a wet process, for example by dipping the polycarbonate in a silicone bath or by spraying silicone on the polycarbonate. The silicone hardcoat provides abrasion resistance to the polycarbonate and may also include a constituent which absorbs UV radiation.
The above methods of treating polycarbonates, however, suffer from certain disadvantages. For example, PECVD still does not generally provide a deposition rate which is high enough to be commercially viable for many applications involving polycarbonates coated with UV absorbing and abrasion resistant layers. With respect to silicone hard coating, this process is also relatively slow, since the silicone hardcoat must be dried and cured which can take a few hours. Silicone hardcoating has additional disadvantages including a limited shelf life of the solution, the generation of waste chemicals, and a potentially nonuniform thickness due to migration of the fluid coating during drying and curing.
It would be desirable, therefore, to have a method of forming multilayer articles which was effective at protecting the article from abrasion and UV radiation and which could be executed rapidly and effectively to reduce manufacturing costs.
According to an exemplary embodiment of the invention, a method of forming a plurality of layers on an article comprises the steps of flowing a plasma gas in at least one plasma generation chamber, the at least one plasma generation chamber being in communication with a deposition chamber, the deposition chamber having a lower pressure than the at least one plasma generation chamber, the article being disposed in the deposition chamber, generating at least one arc in the at least one plasma generation chamber to create at least one plasma which flows into the deposition chamber, injecting a first material into the at least one plasma to form a first layer on the article, and injecting a second material into the at least one plasma to form a second layer on the first layer, the second material comprising a gaseous reagent.
The invention also relates to an article of manufacture comprising a substrate; an interlayer disposed on the substrate, the interlayer comprising a polymerized organic material; a second layer disposed on the interlayer, the second layer comprising an inorganic ultraviolet absorbing material; and a third layer disposed on the second layer, the third layer comprising an abrasion-resistant material. The interlayer may comprise a polymerized organosilicon material or a polymerized hydrocarbon material, for example. The second layer may comprise a metal oxide or sulfide, for example. The third layer may comprise an oxidized organosilicon material, for example.
According to exemplary embodiments of the invention, the three layers can be applied successively in a short time, due to relatively high deposition rates, e.g. about 5-30, typically 6-15 microns/minute for the interlayer, about 2-8, typically 5-8 microns/minute for the UV absorbing layer, and about 5-20, typically 12-15 microns/minute for the abrasion resistant layer. For example, the three layers can be applied successively in a total deposition time of less than 45 seconds, without cooling between layers. The method can produce articles having a high UV absorbance and a high abrasion resistance. The method also allows relatively large surface areas to be coated with the use of a divergent nozzle.